Japanese children who were breastfed for at least 6 months had a significantly lower risk of overweight and obesity at ages 7 and 8 years than did those who were formula fed, according to an analysis of more than 60,000 children that was reported online August 12 in JAMA Pediatrics.
This association was strongest for obesity. In particular, exclusive breastfeeding for at least 6 months was associated with a 45% decreased risk of childhood obesity and a 15% decreased risk of childhood overweight, said Michiyo Yamakawa of the department of epidemiology, Okayama (Japan) University, and her associates.
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Exclusive breastfeeding for at least 6 months was associated with a 45% decreased risk of childhood obesity, said Michiyo Yamakawa.
Many previous studies have shown that breastfeeding exerts a protective effect against childhood obesity, with most reporting a 15%-20% reduction in risk. But a few recent studies, including the only other study to assess this relationship in an Asian population, concluded that there was no protective effect and that findings to the contrary most likely reflect confounding by other factors associated with breastfeeding, such as socioeconomic status, dietary habits, physical activity levels, and such maternal factors as smoking status.
Ms. Yamakawa and her colleagues examined this issue using a large, nationwide database that allowed for control of many important confounders. The ongoing Longitudinal Survey of Babies in the 21st Century has collected reports from parents on family circumstances, child-rearing practices, and children’s health and development throughout Japan since 2001 (JAMA Pediatr. 2013 [doi:10.1001/jamapediatrics.2013.2230]).
For this study, the researchers focused on 29,907 7-year-old and 30,780 8-year-old children whose families participated in the surveys when the children were 6 months of age. All the study subjects were singleton infants born at term.
The data allowed the investigators to calculate the children’s current body mass index, and also included their television viewing time; their computer game–playing time; the parents’ knowledge of nutritional matters; and maternal educational attainment, smoking status, and employment status.
More than 20% of this study population had been exclusively breastfed for at least 6 months, and more than 70% had been partially breastfed for that length of time. Only 5%-6% of the children had been exclusively formula-fed. Japanese society strongly promotes breastfeeding, which may account for the difference in prevalence between this study population and typical Western populations, they noted.
In the 7-year-old group, 7.3% were overweight and 2.1% were obese. The prevalence of both of overweight and obesity decreased as the duration of breastfeeding increased, showing a dose-response relationship.
After the data were adjusted to account for several confounders, the protective effect of breastfeeding against overweight and obesity still remained significant.
The results were similar in the 8-year-old group, in which 7.8% were overweight and 1.9% were obese. Here again the prevalence of both conditions decreased as the duration of breastfeeding increased, and the association remained significant even after adjustment for several confounders.
This study was supported by grants from the Japanese Ministry of Health, Labour, and Welfare, and the Sumitomo Foundation. No financial conflicts of interest were reported.